WASHINGTON, U.S. - Late on Monday, U.S. President Donald Trump’s daughter-in-law and Donald Trump Jnr’s wife Vanessa Trump was rushed the hospital in New York after she was exposed to a suspicious ‘white powder.’

Police sources said that Donald Trump Jnr’s wife opened an envelope reportedly addressed to her husband that contained the unidentified white, powdery substance.

Police officials said that she opened the letter at 10 am (2 am AEDT) at an East 54th Street apartment on the Upper East Side of Manhattan and was taken to a local hospital as a precaution.

So far, officials have not clarified what the substance was.

The police added that the letter was mailed to the couple’s apartment and addressed to Trump’s 40-year-old son.

According to reports, after the envelope was opened, three people at the residence, including Vanessa, were taken to New York-Presbyterian/Weill Cornell Medical Center as a precaution.

Later in the day, a New York City Police Department spokesman said that Vanessa was coughing and complained of nausea after being exposed to the substance.

Meanwhile, the New York City Fire Department said in a statement that there was no indication anyone suffered injuries.

Further, the department also said the white powder did not appear to be a hazardous material or biological agent.

However, sources later quoted investigators as determining that the substance inside the envelope was cornstarch.